FXUS64 KSHV 081349 AAA
AFDSHV
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SHREVEPORT LA
749 AM CST TUE DEC 8 2009
...A QUICK UPDATE TO THE FORECAST WILL BE COMING...
.DISCUSSION...
IT APPEARS AS IF THE WARM FRONT IS FINALLY STARTING TO MOVE
NORTHWARD...ALBEIT SLOWLY.
THE LATEST SURFACE ANALYSIS HAS THE FRONT STRETCHED NEAR A LAKE
CHARLES LOUISIANA...TO NATCHEZ MISSISSIPPI LINE. WITH ONLY
SCATTERED SHOWERS NOTED ON RADAR THIS MORNING...I THINK IT WILL
ONLY BE A MATTER OF TIME BEFORE THE WARM FRONT STARTS MOVING NORTH
IN EARNEST. IT STILL LOOKS LIKE THE MAIN STORM SYSTEM WILL MOVE
INTO OUR CORNER OF THE WORLD CLOSE TO NOON.
FOR THE MOST PART...THE FORECAST APPEARS TO BE ON TRACK. I HAVE
UPDATED THE HOURLY TEMPERATURE AND DEWPOINT GRIDS BASED ON
OBSERVED TRENDS. AFTERNOON WEATHER AND POP GRIDS HAVE ALSO BEEN
SIMPLIFIED WITH THIS UPDATE...PRIMARILY FOR TEXT PRODUCTS.
ISC GRIDS HAVE BEEN SENT AND SHOULD BE UPDATED ON THE INTERNET. AN
UPDATED SUITE OF PRODUCTS WILL BE ISSUED SHORTLY. /21/
&&
.PREV DISCUSSION... /ISSUED 340 AM CST TUE DEC 8 2009/
SHORT TERM /TODAY THROUGH THURSDAY/...
A COMPLEX AND TRICKY FORECAST APPEARS TO BE ON TAP FOR THE FORECAST
AREA THIS MORNING...ESPECIALLY OVER THE NEXT 24 HOURS.
AREA RADARS SHOW POCKETS OF CONVECTION EARLY THIS MORNING...THANKS
AT LEAST IN PART TO WIDESPREAD ISENTROPIC FORCING IN PLACE OVER THE
REGION. A LOOK AT THE SURFACE MAP SHOWS A NORTHWARD MOVING BOUNDARY
STRETCHED NEAR A BEAUMONT TEXAS TO VILLE PLATTE AND AMITE LOUISIANA
LINE AT 3 AM. WATER VAPOR IMAGERY SHOWS A DEEPENING STORM SYSTEM
ALOFT NEARING THE FOUR CORNERS REGION. THIS FEATURE HAD A RATHER
COMPLEX FRONTAL SYSTEM...WHICH WILL ALSO PLAY A ROLE IN THE SHORT
TERM PORTION OF THE FORECAST.
HERE'S WHAT WE KNOW...
THE SURFACE BOUNDARY TO OUR SOUTHEAST IS FORECAST TO CONTINUE
LIFTING NORTH/WEST OVER THE REGION THIS MORNING. THIS IS IN
RESPONSE TO AN AMPLIFICATION OF THE UPPER-LEVEL FLOW PATTERN DUE TO
THE EASTWARD-MOVING UPPER-LOW. LOW-LEVEL GULF MOISTURE IS FORECAST
TO STREAM INTO THE REGION SOUTH OF THIS BOUNDARY ON THE HEELS OF A
STRONG 850MB JET.
AS THE STORM SYSTEM TO OUR WEST NEARS OUR REGION TOWARD LUNCHTIME...
KINEMATIC FIELDS AT ALL LEVELS OF THE ATMOSPHERE SHOULD STRENGTHEN.
AMPLE UPPER-LEVEL DIFFLUENCE IN THE 500-200MB LAYER SHOULD BE
PRESENT A 130 KNOT /OR MORE/ 250MB JET HEADS INTO THE AREA.
BOUNDARY LAYER WINDS MAY APPROACH 60 OR 70 KNOTS AS WELL...WHICH
WILL CONTINUE TO PUMP PLENTY OF MOISTURE INTO OUR AREA. PLENTY OF
LOW-LEVEL WIND SHEAR WILL BE IN PLACE TO ALLOW ORGANIZED CONVECTION
TO DEVELOP THIS AFTERNOON...AND THE POSSIBILITY FOR SEVERE WEATHER.
LATEST MODEL GUIDANCE INDICATES SURFACE TO 1 KM HELICITY VALUES WILL
LIKELY EXCEED 300 M2/S2...ESPECIALLY IN VICINITY OF THE SURFACE
BOUNDARY.
THANKS TO AMPLE CLOUD COVER AND ONGOING RAIN...INSTABILITY WILL BE
AT A MINIMUM. STILL...WITH LOW-LEVEL WIND SHEAR VALUES THIS
STRONG...THE RISK OF SEVERE WEATHER CANNOT BE IGNORED. THE LACK OF
INSTABILITY WILL PROBABLY LIMIT THE CONVECTIVE COVERAGE SOMEWHAT...
BUT IS NOT EXPECTED TO REALLY INHIBIT DEVELOPMENT. MANY SEVERE
WEATHER EVENTS HAVE OCCURED IN A HIGH SHEAR/LOW INSTABILITY
ENVIRONMENT...SOME IN RECENT MEMORY.
THE PROBLEM IS THE RAIN. IF THE RAIN AREA EXPANDS...THE LOCATION OF
THE SURFACE BOUNDARY WILL LIKELY BE REINFORCED. THIS WILL KEEP ANY
SEVERE WEATHER RISK FURTHER SOUTH AS THE BOUNDARY WILL NOT BE
ALLOWED TO MOVE NORTHWARD. ON THE OTHER HAND...IF ONGOING
CONVECTION DIMINISHES SOMEWHAT OR THE UPPER-LEVEL SYSTEM IS STRONGER
THAN ANTICIPATED...WE MAY SEE THE BOUNDARY MOVE FURTHER NORTH AND
CURRENTLY FORECAST. BOUNDARY LOCATION WILL ALSO LARGELY DETERMINE
HIGH TEMPERATURES FOR TODAY...WITH AS MUCH AS A 10 DEGREE SPREAD
BETWEEN MODEL GUIDANCE /ESPECIALLY WESTERN AND NORTHERN AREAS/.
AFTER COLLABORATION WITH THE STORM PREDICTION CENTER...I PLAN ON
CONTINUING A MORE CONSERVATIVE APPROACH. I FEEL THE BOUNDARY MAY
MAKE IT AS FAR NORTH/WEST AS A WELLS TEXAS TO HUTTIG ARKANSAS LINE.
THIS IS NOT QUITE AS GANGBUSTERS AS THE GFS...BUT SLIGHTLY MORE
AGGRESSIVE THAN THE NAM. ANY SEVERE WEATHER RISK WOULD BE ALONG AND
SOUTH OF THIS LINE...ESPECIALLY IF STORMS INTERSECT THE SURFACE
BOUNDARY. TORNADOES AND DAMAGING WINDS APPEAR TO BE THE MAIN SEVERE
WEATHER IMPACTS.
SHOWERS AND THUNDERSTORMS WILL END FROM WEST TO EAST...AS THE STORM
SYSTEM MOVES THROUGH THE REGION LATE TONIGHT. WE MAY SEE SOME
LINGERING CLOUD COVER /ESPECIALLY OVER NORTHERN AND EASTERN AREAS/
INTO WEDNESDAY...BUT VERY LITTLE...IF ANY...ADDITIONAL RAINFALL IS
EXPECTED IN WAKE OF THE COLD FRONT. A LAKE WIND ADVISORY COULD BE
REQUIRED BY LATE TONIGHT AS GUSTY NORTH WINDS ARE EXPECTED IN WAKE
OF THE FRONT. I WILL KEEP WIND SPEEDS BELOW ADVISORY CRITERION FOR
NOW AND LET THE DAYSHIFT CREW MAKE THE FINAL JUDGEMENT CALL BASED ON
THE LATEST MODEL DATA.
ONCE THE FRONT EXITS THE REGION...LOOK FOR HIGH PRESSURE AND A ZONAL
FLOW ALOFT TO KEEP WEATHER CONDITIONS DRY INTO THURSDAY.
TEMPERATURES WILL REMAIN ON THE COOL SIDE AND BELOW EARLY DECEMBER
NORMALS.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
IT STILL LOOKS LIKE AN UNSETTLED WEATHER PATTERN WILL CONTINUE
ACROSS THE FORECAST AREA FOR DAYS 4 THROUGH 7.
SURFACE HIGH PRESSURE IS FORECAST TO START SLIDING EAST OF THE
TENNESSEE VALLEY THURSDAY NIGHT. AS THIS OCCURS...ISENTROPIC
UPGLIDE SHOULD ONCE AGAIN COMMENCE OVER THE REGION. IT APPEARS AS
IF MOST OF THE RAIN SHOULD HOLD OFF UNTIL AFTER MIDNIGHT FRIDAY...
WHEN LOWER CONDENSATION PRESSURE DEFICITS START MOVING NORTHWARD
ACROSS OUR AREA.
RAIN WILL PROBABLY CONTINUE OFF-AND-ON OVER MOST OF OUR AREA THROUGH
THE DAY FRIDAY...AND PROBABLY FRIDAY NIGHT. A RATHER SUBTLE
SHORTWAVE TROUGH IS FORECAST TO AID IN THE DEVELOPMENT OF A WAVE OF
LOW PRESSURE OVER THE NORTHWESTERN GULF FRIDAY NIGHT. MUCH OF THE
PRECIPITATION SHOULD FINALLY TAPER FROM THE WEST SATURDAY AS THIS
SYSTEM MOVES EAST OF THE AREA.
SUNDAY AND MONDAY ARE MORE TRICKY...AS THE SEEMINGLY PREDICTABLE
ISENTROPIC FORCING APPEARS TO TAKE A BREAK. WEAK SHORTWAVE TROUGHS
ARE FORECAST TO CONTINUE TRAVERSING THE REGION IN THE BROAD
SOUTHWESTERLY FLOW ALOFT. ANOTHER COLD FRONT IS FORECAST TO DROP
SOUTHWARD TOWARD THE REGION DURING THIS PERIOD...BUT MAY NOT MAKE IT
MUCH FURTHER SOUTH THAN IH-40 THANKS TO THE UPPER FLOW. I HAVE
INCLUDED SMALL PRECIPITATION PROBABILITIES DURING THIS TIME PERIOD
WITH THIS PACKAGE. HOWEVER...DO NOT BE SURPRISED IF THINGS CHANGE
OVER THE NEXT FEW DAYS. /21/
AVIATION...
POOR FLIGHT CONDITIONS WILL PERSIST THROUGHOUT MUCH OF THE TAF
PERIOD FOR CIGS AND VSBY. LATER TODAY THE BEST CHANCES OF EMBEDDED
THUNDER WILL RESIDE CLOSEST TO THE WARM FRONT...WHICH LIES ALONG THE
GULF COAST THIS EARLY MORNING. VLIFR CIGS AND DENSE FOG ALONG THE
WARM AIR ADVANCING ACROSS E TX/N LA...WITH CONDITIONS IMPROVING
SLIGHTLY ONCE THE SHRA AND EMBEDDED THUNDER DEVELOP ONCE MORE. THIS
NEXT ROUND OF ACTIVITY WILL DIMINISH FROM W TO E LATER THIS
AFTERNOON...IFR CIGS AND POSSIBLY SOME -DZ MAY PERSIST THROUGH THE
EVENING...BEFORE A COLD FRONT SWEEPS THROUGH THE REGION TUESDAY
NIGHT...WITH CIGS/VSBYS IMPROVING MARKEDLY BY 12Z WEDNESDAY. WINDS
WILL VEER FROM EAST TO SSW 5-10KTS AREAWIDE...THEN SHIFTING TO NW
AND GUSTY FROM E TO W 09/06-12Z. /24/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 63 43 48 27 48 / 90 20 10 0 10
MLU 67 45 49 27 48 / 100 50 10 0 10
DEQ 52 36 44 20 47 / 100 10 10 0 0
TXK 53 40 46 22 46 / 90 10 10 0 0
ELD 57 40 47 23 46 / 90 30 10 0 10
TYR 55 41 46 27 49 / 90 10 10 0 0
GGG 58 42 47 27 49 / 100 10 10 0 10
LFK 67 46 53 28 51 / 80 10 10 0 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
&&
$$
PUBLIC FORECASTER... D. BUTTS
AVIATION/FIRE WEATHER FORECASTER... CHATELAIN
